JP2002184896A - Wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that a bonding failure or solder failure occurs, if the thickness of a gold layer is equal on the surface of each of pads on a wiring board where the wire bonding and the solder bonding are made. SOLUTION: The wiring board has a gold layer 8 on the surfaces of wire bonding pads 4 and solder pads 5. The layer 8 has a diffraction intensity proportion of 0.5 or more in a plane (111) to the sum of diffraction intensities in the planes (111), (220), (311) and (222) in the X-ray diffraction. Since the diffraction intensity proportion is set to 0.5 or more in the plane (111) to the sum of the diffraction intensities in the typical five planes, the production of nickel oxides or hydroxides lowering the wire bonding intensity and the solder bonding strength is suppressed to improve both the wire bonding and solder bonding properties.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wiring board on which electronic components such as semiconductor elements, capacitors and resistors are mounted via bonding wires and which is connected to an external electric circuit board such as a motherboard via solder. The present invention relates to a wiring board formed by applying a gold layer to the surface of the wiring layer.

[0002]

2. Description of the Related Art Conventionally, a wiring board on which electronic components such as a semiconductor element, a capacitor element, a resistor, etc. are mounted and connected to an external electric circuit board is generally provided with an insulating base made of an aluminum oxide sintered body and an insulating base. And a plurality of wiring layers made of a high melting point metal material such as tungsten and molybdenum formed from the upper surface to the lower surface of the base.

Further, wire bonding pads for mounting electronic components such as semiconductor elements, capacitors and resistors are formed on the upper surface of the insulating base, and each electrode of the electronic components is electrically connected to a wiring layer via a bonding wire. In addition, solder pads for mounting a wiring board on an external electric circuit board such as a motherboard are formed on the lower surface of the insulating base. Are electrically and mechanically connected to the wiring conductors via solder.

[0004] By mounting the wiring board on which the electronic component is mounted on the external electric circuit board, each electrode of the electronic component is electrically connected to a predetermined external electric circuit board.

In such a wiring board, a nickel layer and a gold plating layer are sequentially formed on the surface of a metallized wiring layer formed on the surface of an insulating substrate, and the nickel layer and the gold layer oxidize the metallized wiring layer. Corrosion is effectively prevented, and the bonding of the bonding wire and the solder to the wire bonding pad and the solder pad is made strong.

However, in such a wiring board, the thickness of the gold layer on the surface of the solder pad on which soldering is performed is limited by the heat and the like required at the time of solder bonding with the external electric circuit board. In order to suppress the formation of a gold-tin intermetallic compound layer which causes a decrease in solder joint strength due to the reaction of tin in the solder, for example, 0.05 to 1
It was necessary to make the thickness relatively small as μm. On the other hand, the thickness of the gold layer on the surface of the wire bonding pad where the wire bonding is performed is to prevent oxidation of the underlying nickel layer and to sufficiently diffuse the metal between the gold layer and the bonding wire to ensure the reliability of the wire bonding. In order to strengthen the bonding, it was necessary to make the thickness relatively large, for example, about 1 to 3 μm or more.

[0007] As described above, a method for making the thickness of the gold layer on the surface of the wire bonding pad connected to the electronic component and the thickness of the gold layer on the surface of the solder pad connected to the external electric circuit board different from each other is as follows. In advance, for example, 0.05-1 μm
After forming a gold layer having a desired thickness necessary for soldering, the surface of the solder pad is covered with a masking sheet or the like so as not to be plated, and again, for example, 1 to 3 μm and a desired thickness required for wire bonding. After forming the gold layer, a method of removing the masking sheet has been conventionally performed.

However, in such a method, the pressure-sensitive adhesive applied to the masking sheet remains on the surface of the gold layer of the solder pad. However, there is a problem in that even if it is applied, this is repelled, the solder wetting property is reduced, and soldering failure is caused.

Therefore, as a method of solving such a problem, a method of using a masking sheet provided with an adhesive only on the periphery of the solder pad and preventing the adhesive from adhering to the surface of the solder pad has been attempted. Have been.

[0010]

However, in the conventional method of making the thickness of the gold layer on the surface of the wire bonding pad and the thickness of the gold layer on the surface of the solder pad different from each other by using such a masking sheet, an insulating substrate is used. At any one of the above sites, the adhesive of the masking sheet remains to a considerable extent, which may cause a problem in appearance.

In order to remove the adhesive residue from such a masking sheet by immersing it in an alkaline solution or the like for a long period of time, pinholes or the like existing in the gold layer formed on the metallized wiring layer are required. Alkaline solution reaches the underlying nickel layer through the defects of, causing deterioration such as formation of a material such as nickel hydroxide that reduces wire bonding and solder wetting, which causes poor wire bonding and soldering There was a problem.

On the other hand, recently, as a type of solder used for connecting a plurality of solder pads formed on the lower surface of a wiring board to each electrode of an external electric circuit board, a general alloy of tin and lead is used. In addition, alloys containing tin as a main component, for example, tin-silver alloys generally called lead-free solders have been used. Since these lead-free solders have a higher melting point than general tin-lead solders, the heat required to connect the wiring layer and each electrode of the external electric circuit board via the solder is also reduced. Requires higher temperatures than tin-lead solders.

In such a case, the appearance defects and the poor soldering caused by the residual adhesive of the masking sheet are more increased than in the case of using a general tin-lead solder. There was also a problem of becoming.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to make the thickness of the gold layer on the surface of the metallized wiring layer in the wire bonding pad and the solder pad different from each other. An object of the present invention is to provide a wiring board which effectively prevents wire bonding failure and soldering failure and has high wire bonding strength and solder bonding strength.

[0015]

Means for Solving the Problems As a result of intensive studies on the above problems, the present inventors have found that wire bonding strength depends on the crystal orientation of the gold layer, especially when the (111) plane crystal orientation is strong. It was found that the strength increased. First, the present inventors investigated the crystal orientation of a conventional gold layer by X-ray diffraction. As a result, five typical faces of the gold crystal, that is, the (111) face and the (20) face
0) plane / (220) plane / (311) plane and (222) plane
The ratio of the diffraction intensity of the (111) plane to the total diffraction intensity of the plane was less than 0.5. Furthermore, among these five planes, the diffraction intensity of the (111) plane and the (200) plane is higher than that of the other planes, and the diffraction intensity of the (111) plane is almost equal to the diffraction intensity of the (200) plane. To the same extent, for example, (1
It has been found that the relative intensity of the (200) plane is 50 to 95 when the diffraction intensity of the 11) plane is 100.

Next, the present inventors investigated the effect of the ratio of the diffraction intensity of the (111) plane to the sum of the diffraction intensities of the five typical planes of the gold crystal on the wire bonding strength. As a result, it was found that the wire bonding strength was excellent when the ratio of the diffraction intensity of the (111) plane to the total of the diffraction intensities of the five typical planes of the gold crystal was 0.5 or more. Furthermore, it has been found that the wire bonding strength is particularly high when the relative intensity of the (200) plane is 5 to 20 when the diffraction intensity of the (111) plane is 100, and the present invention has been completed.

[0017] Of the five typical surfaces of the gold layer, (3
The influence of the diffraction intensity of the 11) plane or the (220) plane on the wire bonding strength was not recognized.

That is, the wiring board of the present invention is a wiring board in which a metallized wiring layer having a wire bonding pad and a solder pad is formed on an insulating base, and the surface of the wire bonding pad and the solder pad has an X-ray (111) plane / (200) plane in diffraction
The ratio of the diffraction intensity of the (111) plane to the sum of the diffraction intensities of the (220) plane, the (311) plane, and the (222) plane is 0.5.
The above-described gold layer is formed by deposition.

In the wiring board according to the present invention, the relative intensity of the (200) plane is 5 to 2 when the diffraction intensity of the (111) plane in X-ray diffraction of the gold layer is 100.
It is characterized by being 0.

The reason why the wire bonding strength is high when the crystal structure of the gold layer on the surface of the metallized wiring layer has a strong (111) plane orientation has not yet been elucidated in detail, but is based on the following reasons. I think that the. When comparing the (111) plane and the (200) plane observed by X-ray diffraction, in gold having a face-centered cubic structure, the higher the proportion of the (111) plane having a higher atomic density is, the higher the atomic density is. Oxygen and moisture are less likely to oxidize and corrode the underlying nickel through the gold layer, or the nickel of the underlying nickel layer is less likely to diffuse to the surface of the gold layer due to heat or the like than those having many low (200) planes. For this reason, it is considered that nickel oxide or hydroxide that hinders metal bonding is not easily formed at the interface between the bonding wire and the gold layer where metal bonding is performed.

On the other hand, a gold layer having a strong (111) plane orientation in the solder pad also has a function of suppressing the formation of oxides and hydroxides that inhibit metal bonding at the interface between the solder and the gold layer in the same manner as described above. Therefore, there is an effect that the solderability is improved particularly in a soldering method that does not use a flux.

That is, according to the wiring board of the present invention, X
(111) plane / (200) plane / (22)
Since a gold layer having a ratio of the diffraction intensity of the (111) plane to 0.5 or more with respect to the sum of the diffraction intensities of the (0) plane / (311) plane and the (222) plane is formed, the wire bonding pad and the solder pad are formed. In addition, it is possible to effectively suppress the formation of nickel oxide, hydroxide, and the like, which cause a reduction in wire bonding strength and solder bonding strength.

Further, the above gold layer was subjected to X-ray diffraction (1
If the relative intensity of the (200) plane is 5 to 20 when the diffraction intensity of the 11) plane is 100, the atomic density is higher than the ratio of the (200) plane having the lower atomic density (11).
1) Since the ratio of the surface is further increased, the formation of nickel oxide and hydroxide can be more effectively suppressed. Therefore, the thickness of the gold layer is, for example, 0.3 to 1
Even if the thickness is relatively small, the wire bonding strength can be prevented from lowering, so that the thickness of the gold layer of the wire bonding pad and the thickness of the gold layer of the solder pad can be reduced to the thickness required for the solder pad. , For example, 0.3-1
Excellent wire bonding and soldering properties can be obtained even if the thickness is the same in the range of μm, and the thickness of the gold layer on the surface of the wire bonding pad and the solder pad differs using a masking sheet. It is possible to avoid poor appearance, poor wire bonding and poor soldering caused by the residue of the adhesive on the masking sheet and the alkaline solution for removing the adhesive.

[0024]

Next, the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a cross-sectional view showing an example of an embodiment in which the wiring board of the present invention is applied to a semiconductor element housing package for housing a semiconductor element.
2 is a metallized wiring layer. The insulating substrate 1 and the metallized wiring layer 2 form a wiring board on which the semiconductor element 3 is mounted.

The insulating substrate 1 is made of an electrically insulating material such as an aluminum oxide sintered body, an aluminum nitride sintered body, a mullite sintered body, a silicon carbide sintered body, a glass ceramic sintered body, and the like. A large number of metallized wiring layers 2 are formed from the mounting portion to the lower surface. The insulating substrate 1 has a mounting portion for mounting the semiconductor element 3 on the upper surface, and the wire bonding pad 4 exposed on the mounting portion has a semiconductor element. 3
Are electrically connected via bonding wires 6 and solder pads 5 led out to the lower surface of insulating base 1.
Is electrically connected to a wiring conductor of an external electric circuit board via solder or the like.

When the insulating base 1 is made of, for example, an aluminum oxide sintered body, a suitable organic binder and a solvent are added to a raw material powder such as aluminum oxide, silicon oxide, calcium oxide, magnesium oxide, etc. and mixed to form a slurry. A ceramic green sheet (ceramic green sheet) is obtained by forming the ceramic slurry into a sheet by employing a sheet forming technique such as a doctor blade method or a calender roll method which is well known in the art. It is manufactured by cutting and punching ceramic green sheets into appropriate shapes and laminating a plurality of them, and finally firing the laminated ceramic green sheets at a temperature of about 1600 ° C. in a reducing atmosphere. .

The metallized wiring layer 2 has a function of connecting each electrode of the mounted semiconductor element 3 to an external electric circuit board. For example, the metallized wiring layer 2 is made of a high melting point metal powder such as tungsten, molybdenum and manganese. A metal paste obtained by adding and mixing an appropriate organic binder and a solvent to the high melting point metal powder is applied to a ceramic green sheet serving as the insulating substrate 1 in a predetermined pattern by a known screen printing method in advance. 1 from the mounting portion of the semiconductor element 3 on the upper surface to the lower surface.

The metallized wiring layer 2 has a wire bonding pad 4 at a part exposed on the surface of the insulating substrate 1 for connecting the semiconductor element 3 to the upper surface of the insulating substrate 1 via the bonding wire 6. 1 has a solder pad 5 led out for connecting an external electric circuit board via solder or the like to the lower surface thereof.

As shown in FIG. 2, a nickel layer 7 and a gold layer 8 are sequentially coated on the wire bonding pad 4 and the solder pad 5 of the metallized wiring layer 2 by plating or the like. It is formed.

The nickel layer 7 functions as a base metal for depositing the gold layer 8 on the metallized wiring layer 2.
By adopting the electrolytic plating method, specifically, the insulating substrate 1 having the metallized wiring layer 2 is made of nickel sulfate 200
g / L · nickel chloride 50 g / L · boric acid 40 g / L in an electrolytic nickel plating solution and apply a predetermined plating power through a plating jig or the like.
Is formed on the surface of the metallized wiring layer 2 by depositing nickel on the metallized wiring layer 2.

The thickness of the nickel layer 7 is 0.5 μm from the viewpoint of completely covering the metallized wiring layer 2 and firmly joining the bonding wire 6 to the wiring layer.
Since the internal stress increases when the thickness exceeds 15 μm, the thickness is desirably 15 μm or less from the viewpoint of the adhesion strength to the metallized wiring layer 2. Therefore, the nickel layer 7 has a thickness of 0.5 to 15 μm.
Is preferably set in the range.

Next, a gold layer 8 is formed on the surface of the nickel layer 7 so as to have a predetermined thickness. The gold layer 8 can prevent the nickel layer 7 from being oxidized and corroded. Has excellent bonding and solder wetting properties, so that the bonding pad 5 and the bonding wire 6,
And a function of firmly joining the solder pad 5 and solder or the like.

According to the present invention, the gold layer 8 formed on the nickel layer 7 of the wire bonding pad 4 and the solder pad 5 of the metallized wiring layer 2 has the (111) plane, the (200) plane, (220) plane ・ (31)
The sum of the diffraction intensities of the (1) plane and the (222) plane is (1)
11) It is important that the ratio of the diffraction intensity of the plane is 0.5 or more. The crystal plane of the surface of the gold layer 8 on the wire bonding pad 4 and the solder pad 5 has a high atomic density (111).
When the ratio is large, the formation of nickel oxide or hydroxide which causes a decrease in wire bonding strength and solder bonding strength is suppressed, and the bonding between the bonding pad 5 and the bonding wire 6 and the solder pad 5 and the solder Can be strengthened.

Further, the (111) plane of the gold layer 8 and the (20)
By setting the relative intensity of the (200) plane to 5 to 20 when the diffraction intensity of the (0) plane is set to 100 when the diffraction intensity of the (111) plane is 100, the formation of nickel oxide and hydroxide is further suppressed. Therefore, even if the thickness of the gold layer 8 is relatively thin, for example, 0.3 to 1 μm, which is necessary for soldering, wire bonding defects are less likely to occur, and the wire bonding pad 4
Even when the thickness of the gold layer 8 in the solder pad 5 is the same as each other, both the wire bonding property and the solderability can be improved.

The gold layer 8 having a strong (111) plane orientation is made of, for example, gold potassium cyanide / potassium cyanide / potassium dihydrogen phosphate / diammonium hydrogen phosphate / ammonium sulfate when formed by electrolytic plating. It is preferable to use an electrolytic gold plating bath in which a heavy metal such as lead and an amino acid-based reagent are added to the solution. In such an electrolytic gold plating bath, the deposition state of gold is adjusted by combining three kinds of complexing agents, potassium dihydrogen phosphate, diammonium hydrogen phosphate, and ammonium sulfate, and the crystal structure of the gold layer 8 is It is considered that the (111) plane orientation becomes stronger.

Further, regardless of the plating solution composition and the plating conditions, based on a conventionally well-known gold plating solution composition, for example, two to three kinds of complexing agents are used and various combinations and concentrations are examined. It may be carried out by adding or adding various additives, while it may be controlled by plating conditions such as current density, current waveform, distance between electrodes, bath temperature, pH, stirring speed and the like.

The crystal orientation of the gold layer 8 may be measured by a conventionally well-known X-ray diffraction method.
(200) plane, (220) plane, (311) plane, and (2) plane
The sum of the diffraction intensities of the (22) plane and the diffraction intensity of the (111) plane are compared, and the ratio of the diffraction intensity of the (111) plane may be 0.5 or more.
When the relative intensity of the diffraction intensity of the (200) plane is 5
It should be ~ 20.

On the other hand, the thickness of the gold layer 8 is
The thickness is preferably 0.3 μm or more from the viewpoint of preventing oxidative corrosion and increasing the wire bonding strength, and is preferably 1 μm or less from the viewpoint of suppressing the formation of a gold-tin intermetallic compound and increasing the solder bonding strength. Therefore, it is desirable that the thickness of the gold layer 8 be in the range of 0.3 to 1 μm.

From the viewpoint of securely and firmly bonding the bonding wire 6 to the predetermined wire bonding pad 4, the surface morphology of the gold layer 8 is determined by averaging the waviness in a range of 100 μm square measured by an atomic force microscope. The height is 200 nm to 800 nm, and the average height of the roughness in the range of 10 μm square within the range of 100 μm square is 40 to 20.
Desirably, it is 0 nm. This is because when the bonding wire 6 is connected to the wire bonding pad 4 by an ultrasonic method, the loss of frictional energy is suppressed, the bonding area of the bonding wire 6 is increased, and the bonding wire 6 is securely and securely connected to the wire bonding pad 4. This is for firm bonding.

On the other hand, the gold layer 8 has a Vickers hardness of 50
If it is less than 100 mm, the gold layer 8 is greatly deformed by the bonding load applied during wire bonding, so that the bonding wire 6 cannot be firmly joined to the wire bonding pad 4. When the bonding wire 6 slips on the surface of the gold layer 8, sufficient frictional energy cannot be obtained. Therefore, it is desirable that the gold layer 8 has a Vickers hardness of 50 to 100.

The above nickel layer 7 and gold layer 8
In order to prevent the metallized wiring layer 2 exposed on the surface of the insulating substrate 1 from being oxidized and corroded, the metallized wiring layer 2 may be formed on the metallized wiring layer 2 other than the wire bonding pads 4 and the solder pads 5 by adhesion.

The lid 9 on which the semiconductor element 3 is mounted is joined to the upper surface thereof via a sealing material made of resin, glass, brazing material or the like.
Thus, the semiconductor element 3 is hermetically sealed.

The lid 9 is made of a ceramic material such as an aluminum oxide sintered body, a mullite sintered body, an aluminum nitride sintered body, or an iron-nickel-cobalt alloy or an iron-based material.
If it is made of a metal material such as a nickel alloy, for example, if it is made of an aluminum oxide sintered body, a material powder such as aluminum oxide, silicon oxide, magnesium oxide, calcium oxide, etc. should be formed by a conventionally known press molding method. And formed by baking it at a temperature of about 1500 ° C.

Thus, according to the wiring board of the present invention, the electrodes of the semiconductor element 3 are electrically and mechanically connected to the wire bonding pads 4 exposed on the mounting portion of the semiconductor element 3 on the upper surface of the insulating base 1 via the bonding wires 6. After connection, a lid 9 made of metal or ceramics is joined to the upper surface of the insulating base 1 via a sealing material such as glass, resin, brazing material, or the like. The semiconductor element 3 is hermetically housed, and a low-melting-point solder paste is applied on the surface of the solder pad 5 led out to the lower surface of the insulating base 1 by printing or the like, and a high-melting-point solder ball is placed thereon. The semiconductor device as a product is completed by melting only the low-melting-point solder by reflow to form solder bumps.

The wiring board of the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the gist of the present invention. For example,
Although the gold layer is formed by the electrolytic plating method in the example of the above embodiment, it may be formed by another method such as an electroless plating method. Further, the wiring substrate of the present invention is applied to a semiconductor element housing package for housing a semiconductor element, but may be applied to other uses such as a hybrid integrated circuit board.

[0047]

According to the wiring board of the present invention, the (111) plane, the (200) plane, the (220) plane, and the
Since a gold layer having a ratio of the diffraction intensity of the (111) plane to 0.5 or more with respect to the sum of the diffraction intensities of the (311) plane and the (222) plane was formed, the wire bonding strength was applied to the wire bonding pad and the solder pad. In addition, it is possible to effectively suppress the formation of nickel oxide, hydroxide, and the like, which cause a decrease in solder joint strength.

Further, the gold layer was subjected to X-ray diffraction (1
If the relative intensity of the (200) plane is 5 to 20 when the diffraction intensity of the 11) plane is 100, the atomic density is higher than the ratio of the (200) plane having the lower atomic density (11).
1) Since the ratio of the surface is further increased, the formation of nickel oxide and hydroxide can be more effectively suppressed. Therefore, the thickness of the gold layer is, for example, 0.3 to 1
Even if the thickness is relatively small, the wire bonding strength can be prevented from lowering, so that the thickness of the gold layer of the wire bonding pad and the thickness of the gold layer of the solder pad can be reduced to the thickness required for the solder pad. , For example, 0.3-1
Excellent wire bonding and soldering properties can be obtained even if the thickness is the same in the range of μm, and the thickness of the gold layer on the surface of the wire bonding pad and the solder pad differs using a masking sheet. It is possible to avoid poor appearance, poor wire bonding and poor soldering caused by the residue of the adhesive on the masking sheet and the alkaline solution for removing the adhesive.

Further, since the formation of nickel oxide, hydroxide or the like which hinders the solder joint is further suppressed, a soldering method using no flux or a tin-free solder generally called lead-free solder is used. Even if the amount of heat load when connecting the wiring board to the external electric circuit board via solder increases by using silver-based solder, the wiring board can be connected very easily and reliably via solder. And the long-term reliability of the solder joint can be improved.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of an embodiment of a wiring board of the present invention.

FIGS. 2A and 2B are enlarged cross-sectional views of main parts of the wiring board shown in FIG. 1;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Insulating base 2 ... Metallized wiring layer 4 ... Wire bonding pad 5 ... Solder pad 8 ... Gold layer

Claims (2)

[Claims] 1. A wiring board in which a metallized wiring layer having a wire bonding pad and a solder pad is formed on an insulating base, and the surface of the wire bonding pad and the solder pad is subjected to (11) in X-ray diffraction.
A gold layer having a ratio of the diffraction intensity of the (111) plane to 0.5 or more with respect to the sum of the diffraction intensities of the 1) plane, the (200) plane, the (220) plane, the (311) plane, and the (222) plane is formed. A wiring board characterized by being made. 2. (111) in X-ray diffraction of the gold layer
2. The wiring substrate according to claim 1, wherein the relative intensity of the (200) plane is 5 to 20 when the diffraction intensity of the plane is 100.